Re: Streaming of WebVTT

On Thu, Jul 26, 2012 at 12:52 AM, Cyril Concolato
<cyril.concolato@telecom-paristech.fr> wrote:
> Le 7/25/2012 4:40 PM, Glenn Maynard a écrit :
>
> On Wed, Jul 25, 2012 at 9:18 AM, Cyril Concolato
> <cyril.concolato@telecom-paristech.fr> wrote:
>>
>> I'm trying to integrate WebVTT content in streaming context (MP4, RTP,
>> DASH, MPEG-2 ...) in general. Aside from the problem of random access points
>> that I mentionned in my previous email [1], there is a problem with the fact
>> that the "WEBVTT" string has to be at the beginning of the file. Consider
>> the following case, I have a live event and I want client to connect to an
>> HTTP-delivered WebVTT resource, I'd like to update that resource from time
>> to time (removing old cues, adjusting times and adding new cues) and enable
>> both clients already connected to get the update and for new clients to get
>> the new content. That same file has to have the "WEBVTT" string for new
>> clients, but cannot be used as is for the already connected client (I'll
>> have to strip off the "WEBVTT" string). What is the use of that string? Is
>> it really needed given that many resources on the web don't use magic
>> numbers (HTML, XML, SRT, SVG, ...)?
>
>
> You'll need the ability to deal with "header" data anyway.  There have been
> proposals for adding headers for metadata, default cue settings, inline CSS,
> and so on.  It may be a while if any of them are implemented, but please try
> to avoid designing a system that expects WebVTT to be a headerless format.
>
> Thanks for your comment. I wasn't aware of these proposals. Would you have a
> link to them?
> Of course, if the header is meaningful, I agree it makes sense to keep it.
> In all the technologies I mentioned, there is a way to carry headers (stsd,
> sdp, initialization segment, descriptors ...). I was just wondering if there
> was a real need to have it for WebVTT. If I'm correct, according to the
> current syntax in WebVTT, the header can only be one line of text. Is that
> correct?

No, not quite. Everything until the first empty line is regarded as
the header. There is likely setup information in there as for any
other codec. You're best off defining a streaming approach similar to
how you do it with a/v streaming formats.

Cheers,
Silvia.

Received on Thursday, 26 July 2012 01:27:27 UTC